An MS/MS analysis is a type of mass-analyzing method using an ion trap mass spectrometer or similar apparatuses. In a typical MS/MS analysis, an ion having a specific mass-to-charge ratio (m/z) is first separated from the material to be analyzed. This ion is called the precursor ion, or the parent ion. Next, the precursor ion thus separated is broken into fragment ions by a collision-induced dissociation (CID) process. Finally, as the dissociation mode varies depending on the structure of the precursor ion, the fragment ions produced by the dissociation process are subjected to a mass-analyzing process to obtain information about the mass and the chemical structure of the ion concerned.
In recent years, such apparatuses have been often used to analyze samples having larger molecular weights and more complex structures (or compositions) than in previous years. Some samples having special characteristics cannot be broken into ions having adequately small weights by a single dissociating step. One method for dealing with such a case is called the MSn analysis, in which the dissociating operation is repeated multiple (n−1) times and the fragment ions produced are subjected to a mass-analyzing process (refer to Patent Documents 1 and 2 for examples). If, as in the previous case, the dissociating operation is performed just once, the mass analysis of the fragment ions can be called the MS2 analysis.
One popular analysis method for deducing the structure of an unknown substance based on data obtained by an MSn analysis is a so-called pattern matching method using a mass spectrum database. The mass spectrum database contains information on a variety of known compounds such as mass-spectral data obtained by a mass-analyzing process using a certain ionization method, names of compounds, molecular weights, compositional formulas, and structural formulas. By performing a pattern matching operation between a mass spectrum of a known compound and mass spectra of unknown compounds under a predetermined search condition, it is possible to identify the substance having a corresponding spectral peak pattern to that of the unknown substances.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. H10-142196
[Patent Document 2] Japanese Unexamined Patent Application Publication No. 2001-249114
Even if such a database is large, not all compounds to be analyzed can be stored. In particular, it is practically impossible to register all the compounds of agrichemicals and/or pharmaceutical compounds to the database library, because many of them have an identical basic skeleton but have different substituted components or substituents (ethyl substitution for methyl, bromine substitution for chlorine for examples). Accordingly, if an unknown substance to be targeted is not registered in the database, it is difficult to deduce the molecular structure of the unknown substance.
To solve the above-described problem, the present invention intends to provide a method of analyzing mass analysis data for easily deducing the structure of an unknown substance based on data obtained by an MSn analysis.